1. Field of the Invention
The present invention relates to a waste collection system for separating liquid waste from solid waste.
2. Description of the Related Art
In modern agricultural production, it has become usual to employ an agricultural establishment as an intensive feeding operation for raising hundreds or even thousands of animals, e.g. hogs, dairy, poultry and beef animals, at a single location. Consequently, large amounts of animal waste matter are produced at such locations, and the disposal of this waste matter in a hygienic and inoffensive manner can be problematic.
It has, for example, been planned to initiate a hog farm containing 2,000,000 hogs, which will produce an amount of waste equivalent to that produced by the city of Los Angeles. The current pig population of North Carolina is four times that number. Recent accidents in North Carolina, in which millions of gallons of pig excreta were released into the countryside, have drawn attention to the problems involved in the disposal of such waste. Applications for permits to construct large piggeries have been denied because of concerns about odours and waste disposal.
Animal waste, including hog manure, has traditionally been disposed of by spreading it over agricultural land as a liquid fertilizer and, for sufficiently large cropped land bases, this method of disposal can be performed safely. However, in areas of high population density or where multiple farms are closely clustered, and the land base is therefore relatively small, problems arise. For example, excess nutrients cannot be absorbed by crops and leach into ground water and surface water.
When land application is prevented, e.g. because the ground is frozen or saturated with water and/or nutrients, the waste must be stored, usually in large pits, with consequential costs and environmental risk.
As an alternative to land disposal, it is also common practice to compost the waste. For this purpose, the waste is separated into solid and liquid by the use of inclined screens, sometimes followed by the use of belt or filter presses. These methods produce an output containing about 45% solid material at best, and this is then mixed with a bulking material to facilitate aeration and an appropriate C:N ratio, and deposited in windows for stabilization, over a period of about 45 to 60 days, by composting. This process does not ensure that pathogens in the waste are killed and the windrows are often odorous and may attract birds, rodents and vermin. The liquid still has to be dealt with through land application. As such, composting does not reduce the need for land application or land area.
The challenges involved in the treatment of animal waste include the destruction of pathogens, the controlled extraction of ammonium and plant nutrients, and the disposal of organic matter.
It is known to collect waste from animal barns by discharging the waste through openings in the barn floor onto a conveyor belt located in a gutter below the barn floor. The conveyor belt carries the waste to a collection point, and the waste may then be taken to a waste processing facility or the waste may be processed on site.
However, the liquid waste and solid waste are not separated and over time the mixing of liquid waste and solid waste impedes the processing of the waste. Furthermore, the mixing of the liquid waste and solid waste may cause the release of gases which are harmful to humans, animals and the environment.
In the inventor's co-pending U.S. patent application Ser. No. 10/119,719 filed on Apr. 11, 2002, the disclosure of which is herein incorporated by reference, there was disclosed an invention based on an appreciation of the fact that the extraction of nitrogen, potassium and phosphorous from animal waste material is substantially enhanced if the treatment is performed promptly after the production of the waste material by the animals. More particularly, the aforesaid application Ser. No. 10/119,719 disclosed a method of processing animal waste in which liquid waste and solid waste are separated, preferably within 12 hours following the production of the waste by the animals, and the liquid waste is processed preferably within 24 hours of the production of waste by the animals.
More particularly, potassium is present in animal waste material in the form of an insoluble potassium urate, and it was found that a substantial amount of the potassium in animal waste material can be extracted in a solid form, as potassium urate, before microbial action breaks down the potassium urate to leave potassium and ammonium in solution. Extracted urates are then available for inclusion in a fertilizer. When the fertilizer is used on land, the microbes in the soil break down these urates, releasing the potassium and ammonia, but at a rate less than that at which these nutrients would be released in the soil if dissolved in water.
Consequently, by extracting ammonium-nitrogen and potassium in the form of urates and/or other compounds from the waste material while they remain in solid, e.g. crystalline form, i.e. before they break down to release these substances, a substantially improved extraction of these substances can be achieved. Therefore, the solids and liquids should be separated as soon as possible after their production by the animals.